Vented two-piece closure

ABSTRACT

The disclosed invention is a plastic liner cap in a two-piece closure on containers for beer, carbonated beverages and the like. The liner cap top panel over the mouth area of the container includes a vent means comprised of an annular channel formed in the cap and a series of spaced vertical slits disposed annularly in the channel. An outer cap of metal includes a tear strip for hand removal of the closure. When the tear strip is initially ruptured, pressure is released through the vent slits and conveyed through the initial rupture of the tear strip. Axial flexing movement of the liner opens or closes the vent slits. The vent means assures positive venting on opening the closure and allows capping of the two-piece closure on the container without registering or orientation of the vents and the tear strip. The liner cap is usable as an independent reclosure device after the container is opened. A second embodiment provides a seal of liner and overcap adjacent the opposite margins of the channel. This minimizes space between the liner and overcap for product to collect and cause a reaction before the container is opened.

United States Paten Burroughs I [54] VENTED TWO-PIECE CLOSURE [72] Inventor: Robert O. Burroughs, Toledo, Ohio [73] Assignee: Owen-Illinois, Inc.

[22] Filed: Jan. 26, 1971 [21] Appl. No.: 109,844

[52] US. Cl ..2l5/56, 215/46 A, 215/40 [51] Int. Cl. ..B65d 51/16 [58] Field of Search ..2l5/46 A, 40, 56, 41, 39; 220/44 {56] References Cited UNITED STATES PATENTS 2,254,815 9/1941 Bamby et a1. ..215/56 3,480,173 11/1969 Wheaton ..2l5/46 A 3,561,631 2/1971 Hatfield ..2l5/46 A Primary Examiner-George T. Hall Attorney-J. R. Nelson and E. .l. Holler Aug. 15,1972

[ 5 7 ABSTRACT The disclosed invention is a plastic liner cap in a twopiece closure on containers for beer, carbonated beverages and the like. The liner cap top panel over the mouth area of the container includes a vent means comprised of an annular channel formed in the cap and a series of spaced vertical slits disposed annularly in the channel. An outer cap of metal includes a tear strip for hand removal of the closure. When the tear strip is initially ruptured, pressure is released through the vent slits and conveyed through the initial rupture of the tear strip. Axial flexing movement of the liner opens or closes the vent slits. The vent means assures positive venting on opening the closure and allows capping of the two-piece closure on the container without registering or orientation of the vents and the tear strip. The liner cap is usable as an independent reclosure device after the container is opened. A second embodiment provides a seal of liner and overcap adjacent the opposite margins of the channel. This minimizes space between the liner and overcap for product to collect and cause a reaction before the container is opened.

29 Claims, 10 Drawing Figures PATENTEBAus 15 m2 SHEET 1 0F 3 INVENTOR. ROBERT O. BURROUGHS.

ATT 'YS.

PATENTED 3,684,119

sum 2 OF 3 INVEN TOR.

ROBE RT 0. BURROUGHS.

MW M1 'aJMw PATENTEDAUG 15 I972 SHEET 3 or 5 INVENTOR.

w WM m w s If A ma Y VENTED TWO-PIECE CLOSURE BACKGROUND OF THE INVENTION The invention relates to two-piece closures of the convenience opening type, sometimes called easy open closures.

In such closures, as is exemplified by the disclosures in copending application of J. D. Hatfield and R. A. Heaton, Ser. No. 825,116, filed May S, 1969, now US. Pat. No. 3,561,631 and commonly owned with the application, a plastic liner cap is interposed between the mouth opening of the container and an outer metal cap telescopically arranged over the mouth of the container and clamped or crimped thereon. The outer metal cap is removable by a pull ring fastened to the end of a scored tear strip in the top panel. The outer cap is removed by grasping the pull ring and lifting it to initiate rupture and tear of the strip in the cap. As the cap becomes loosened at opening, the pressure built up in the container by the product (mostly generated CO pressure) may abruptly propel the loosened cap and liner from the container. Not only is this dangerous, but the product is often sprayed or spilled needlessly.

Various vent means have been devised to relieve this pressure upon initial opening of the tear strip. One such example is disclosed in U. S. Pat. No. 3,480,173 to J. M. Wheaton. This comprises a vent slit centrally located in the top panel of the liner cap. However, in assembling the liner cap and outer metal cap to form the composite two-piece cap at or before capping it onto the container, the tear strip must be oriented with the vent slit to function effectively.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a novel vent means in the two-piece closure of the type mentioned, wherein orientation of vent slits and the tear strip is unnecessary.

Another object of the invention is the provision of such a two-piece closure of the type described in which improved vent action is obtained.

A still further object of the invention is the provision of a seal between the outer and inner cap walls adjacent the vent slits to prevent excessive product accumulation and contamination from occurring between the two cap members; and, further, to provide a means of fastening the outer closure and inner liner members together as an assembled unit prior to capping onto a container.

And, another object of the invention is to provide in certain embodiments thereof a two-piece closure in which the outer closure and inner liner members are fastened together, whereby loosening of the outer member by operation of the tear strip facilitates onepiece removal of the outer closure and liner members upon opening of the container with the advantage of suitable venting of pressure in the case of pressurizable product in the container.

Other objects will be apparent to persons skilled in the art from the drawings in the disclosure of the invention and the detailed description thereof which follows.

DESCRIPTION OF THE DRAWINGS On the Drawings: FIG. 1 is a top plan view, partly broken away, of the two-piece closure assembly of the invention.

FIG. 2 is a sectional elevational view taken along line 2-2 on FIG. 1, in which the closure is secured on a glass container finished prior to the contents within the container being pressurized, whereat the vents are closed.

FIG. 3 is a sectional elevational view similar to FIG.

2, but with the contents in the container being initially pressurized whereat the vents are opened until pressure between the caps is equalized.

FIG. 4 is a sectional elevational view similar to FIG. 3 showing the caps after pressurization of the container. the pressure between the caps and inside the container being equalized, whereat the vents are again closed.

FIG. 5 is a sectional elevational view similar to FIG. 4 showing the outer cap being opened and the container being vented, whereat the vents are opened.

FIG. 6 is a sectional elevational view similar to FIG. 5, but showing the caps after the tear strip of the outer cap is fully opened and all pressure inside and outside the container substantially equalized, whereupon the vents are reclosed.

FIG. 7 is a top plan view, partly broken away, of the two-piece closure of the invention illustrating a heat sealing" embodiment.

FIG. 8 is a top plan view, partly broken away, of the two-piece closure of the invention illustrating an adhesive sealing embodiment.

FIG. 9 is a sectional elevational view like FIG. 2 for the two-piece closure embodiment shown on FIG. 7.

FIG. 10 is a sectional elevational view like FIG. 2 for the closure embodiment shown on FIG. 8.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, FIGS. 1-6, a twopiece closure cap assembly according to the present invention is illustrated as employed on the mouth opening (open end) of a glass container 11; The mouth opening is defined by a top rim or bead 12 having an enlarged side wall flange portion 13 that is tapered downwardly and inwardly from the top edge of the container.

The closure cap comprises an inner liner cap 14 made of an elastomeric material, such as polyethylene, other plastic composition or rubber compound. Cap 14 includes a disc-like top panel portion 15 covering the mouth opening area extending inside rim'12 of the container. Liner cap 14 is retained on the rim finish by a skirt portion 16 that has a smallest diameter on its inside surface slightly less than the exterior diameter of the finish under the head 12 of the container. The skirt portion of 16 of liner cap 14 is integrally joined with the periphery of top panel portion 15 at corner radius 17, and in the illustrated embodiments shown on the drawings, the combination of skirt l6 and corner radius 17 forms a groove receiving the rim 12 of the container adapted for sealing the mouth opening along the top and outside surfaces of the finish 12..

In the top panel portion 15 of the closure embodiment shown on FIGS. 1-6, a continuous depression of circular configuration is molded in the form of a channel means. The channel means may otherwise be provided by removal of plastic material, i.e. casting, cutting, stamping, etc., as shown on FIGS. 9, 10; or may be cast in a raised annular base configuration as shown on FIG. 10. This provides means forming an annularly disposed channel 18 around the top surface of liner cap cap connecting the inside of container 11 to the space within channel 18.

Liner cap 14 is formed in the die such that in the non-pressurized condition on container 11, shown on FIGS. 2 and 6, the top panel 15 is a disc-like portion that is generally horizontal. While in horizontal attitude of panel 15, the vent slits 19 are in a closed position. As will presently be described in connection with the outer cap of the closure, a head space 20 will be provided as the container is pressurized (FIGS. 3 and 4), the head space 20 occurring between the liner cap 14 and center panel 21 of the outer metal cap 22. With pressure generated internallycf the container 11, such as CO pressure, the center panel 21 of closure cap 22 flexes upwardly to the domed, convex position illustrated on FIG. 3. This permits the liner cap 14 to flex upwardly sightly, which causes the vent slits 19' to open or separate such that the pressure gas enters the head space 20 until pressure is equalized on both sides of panel 15. This is shown on FIG. 3. As this pressure equalizes, the top panel 15 returns to a generally horizontal, unflexed position and closes vent slits 19 with pressure on the inside space of the container in equilibrium, or nearly so, with that in the head space 20 between the center panel 21 and top panel 15. (FIG. 4). As will be presently described in more detail, upon tear removal of the outer closure, pressure in head space 20 is vented to atmosphere and the vent slits 19 again opened to suitably vent the container. (See FIG. 5).

Thus, it may be seen that the reciprocal flexing action of top panel 15 of the liner opens and closes vent slits 19 so that the vents function automatically as a valve means operated in response to a pressure differential on opposite sides of the top panel 15 of liner cap 14.

Referring to FIGS. l-6, the outer cap member 22 is made of metal, such as aluminum or tin plate of appropriate gauge or thickness, adapted to be crimped or secured around bead flnish 12 of the container and sealingly attached the liner and closure members about the container mouth. Outer cap 22 has peripheral skirt 23 ending in a rolled lower edge or wire 24. The wire 24 serves as a peripheral bead to retain the skirt 16 of the liner cap 14, thereby retaining the two parts in preassembled fashion before capping on a container 11.

The upper part of the skirt 23 blends with corner radius portion 25 and it in turn is integrally joined with the periphery of top panel 21. A tear strip 29 is formed in top panel 21, across corner radius 25 and skirt 23 by a continuous score line 30, (FIG. 1), such as the illustrated configuration. The score line is formed by working the metal to reduce the thickness along a line, or the score may be made by any means that will otherwise enhance shear properties along a line such that the tear strip may be peeled off the closure by an opening pull ring or tab. The score line is usually formed by a dye while the metal of the closure is in flat blank form.

On the drawing, FIG. 1, score line 30 extends from the base of skirt 23 across the corner radius 25 in two spaced legs or lines which merge beyond the center of the top panel 21 of the cap. A ring pool member 27 has a yoke portion 28 fastened to tear strip 29 by the integral rivet 31 in the segment of metal within the score line 30. The integral rivet 31 in the top panel 21 is flattened (riveted) over yoke 29 of the ring pull.

The liner cap member 14 flts beneath the outer cap member 22 when the top panel 15 is horizontal. In this position, the top of liner cap 14 seals on the inside top surface of the outer cap 22. After the closure is assembled and pressure builds within the container, both the metal central panel 21 and plastic top panel 15 flex upwardly. (See FIG. 3.) This action opens vents l9 and pressure enters the cap head space 20. As the pressure equalizes within space 20 with container pressure, the center panel 21 assumes the convex or domed shape and the top panel 15 returns to flat or horizontal position. (See FIG. 4.) As the liner cap 14 assumes the flat condition, the vent slits 19 are closed as shown on FIG. 4. The pop area 29a (FIGS. 2 and 3) is the small segment of the tear strip adjacent the rivet 31 (under yoke 28 on FIG. 1). At the time the container is to be opened, the top panel 15 is flexed to the domed position. The break of the score line 30 at the pop area vents the pressure in head space 20 to atmosphere. Since the volume in space 20 is small, the initial vent is mild and dry; however, immediately the pressure in the container flexes the liner top panel 15 toward the center panel of the outer cap 22. This opens the vents 19 and internal pressure of the container is equalized with outside pressure. Thereafter, the liner top panel 15 assumes the flat or horizontal position again (FIG. 6).

By having the channel 18 continuous and circular on top panel 15, gases vented in any area where' top panel 15 seals against the outer cap will be conveyed to the pop area of the tear strip. Thus, the vent slits 19 are opened and function for venting internal pressure shortly after opening of the pop area 29a of the tear strip 29.

, As seen on the plan view, FIG. 1, the outer cap 22 need not be oriented to any particular vent opening. Regardless of how the outer cap member 22 is assembled over the liner cap member 14, the pop area 29a (initial opening segment) of the tear strip 29 will lie over the channel means 18 for conducting the vented pressure gas through the pop area opening of the tear strip 29 when the latter is ruptured by lifting the ring pull 27. This is accomplished in design of the closure in which the diameter of the circular channel 18 matches approximately the radius from the cap center at which the pop area of the tear strip is located.

The under surface of metal cap 22, if need be, may be enameled, lacquered, foil coated, or the like, to prevent product contamination in the head space 20 between the liner member 14 and the outer cap member 22.

Another embodiment of the invention is shown on FIGS. 7 and 9. The same outer cap member 22 may be employed. The inner liner cap member 14 includes an inner raised circular rib 32 extending around the inside of channel 18. Rib 32 has a flat circular top surface 33 that engages the underside of top panel 21 of the outer metal cap. Similarly, a second circular rib 34 is provided on the top panel around the outside of channel 18 (see FIG. 5) and includes a flat circular top surface 35. When a pressurized container is vented, the central panel 15 of the liner member 14 is pressed upwardly and the two circular flat surfaces 33 and 35 are pressed against the metal cap 22 to seal off channel 18 from the rest of the head space 20. The flexing of the top panel 15 to a domed (convex) configuration functions for opening and closing of vent slits 19, as described above.

The construction just described may be varied in the following respects. In the assembly of the outer and liner cap members, the circular flat surfaces 33 and 35 of ribs 32 and 34 may be heat sealed to the metal under surface of outer cap 22. This will seal off the channel 18 permanently and accomplish two things: (1) The inner liner cap and outer metal cap members are secured together as a one-piece closure unit and, as such, is readily handled in cap feeding and closing equipment to assure a full cap on the container in production; and (2) The head space is sealed off over channel 18 and contamination of product is less probable in the remaining head space. Only produce passing into channel 18 may come into contact with the overlying small annulus area above the channel.

A third embodiment of the invention is shown on FIGS. 8 and 10. Outer cap member 22 again may be the same as above described, however, in this embodiment the liner cap member 14 is positively adhesively secured to the outer metal cap member 22. As seen on the drawings, a coating of adhesive material is applied to the top of the liner cap member 14 in an annular ring 36 radially inwardly of channel 18 and another annular ring 37 of adhesive is applied radially outwardly from channel 18. The outer and liner cap members 22 and 14 are assembled and the adhesive is activated to secure the two pieces together in the form of a onepiece closure. As mentioned above, the sealing of the liner cap member 14 around the opposite side margins of channel 18 by the adhesive rings 36 and 37 contributes the two-fold accomplishment mentioned in connection with the heat sealing of liner to outer cap; namely, securing liner and outer cap members together as a unit, and sealing head space between the two and reducing possible contamination area between the caps.

While a number of specific embodiments of the invention have been described in detail, it should be apparent that various other modifications could readily be made. Further, specific elements of the described embodiments could readily be combined in different configurations than those illustrated without departing from the spirit of the invention.

Accordingly, while preferred embodiments have been illustrated, it should be understood that it is not intended the invention be necessarily restricted solely thereto, but intend to include all embodiments thereof which would be apparent to those skilled in the art, and which come within the spirit of the scope of our invention.

I claim:

1. A closure for sealing the mouth opening of a container for a pressurizable product, said mouth being formed by a finish rim of the container, comprising a liner having a disc-like portion covering the mouth opening of the container, said liner being comprised of an elastomeric material, channel means formed in said disc-like portion disposed annularly therein and radially inwardly of said finish rim, and plural, spaced apart vent slits axially through the material of said disc-like portion located in said channel means, each said vent slit and channel means cooperating through flexing of said material of said disc-like portion to open and close said vent slits for venting therethrough a pressure existing interiorly of the container, a cap having a top portion overlying said elastomeric liner and a radial annular integral skirt portion surrounding the finish rim and securing the closure on the container, and a rupturable convenience-opening tear strip formed in said top portion of the cap, said strip traversing at least one of said slits and channel means in the underlying disc-like portion of the elastomeric liner.

2. The closure defined in claim 1, wherein the channel means comprises an annular groove in the top surface of said liner disc-like portion, said vent slits each being formed axially through the material in the bottom of the groove.

3. The closure defined in claim 2, wherein the groove cross-sectional profile is arcuate.

4. The closure defined in claim 3, wherein the annular groove is continuous.

5. The closure defined in claim 4, wherein said vent slits are arcsegments in spaced array along said groove.

6. The closure defined in claim 5, wherein the vent slits are of equal length and are at equally spaced apart intervals around said continuous arcuate groove.

7. The closure defined in claim 1, wherein said chan nel means comprises a continuous arcuate groove depressed beneath the exterior surface of the liner top portion and provides a channel for conducting vented pressurized media from inside the container to a location beneath the initially ruptured portion of the tear strip of the outer cap upon opening the closure.

8. The closure defined in claim 1, wherein the liner is attached to the underside of the cap on opposite radially disposed sides of the liner channel means.

9. The closure defined in claim 8, wherein said attachment of liner and cap is by an adhesive applied for sealingly attaching the liner and cap on opposite sides of said channel means of the liner.

10. An elastomeric snap cap liner for use in a closure on a containerhaving a' mouth opening defined by a finish rim comprising a top portion covering the mouth opening, a skirt flange surrounding said rim and joined peripherally at one side with the top portion at a corner radius, said corner radius overlying said container rim, groove means in the top surface of said top portion and disposed inwardly therein of said corner radius, and slit means through the top portion of said liner and disposed in said groove means.

11. The elastomeric snap cap liner defined in claim 10, characterized by the fact that the slit means is openable by a pressure differential built up between the exterior and interior of the container to provide a vent for the container and closed when the pressure in the container is near atmospheric pressure.

12. A liner for a closure covering a container mouth opening comprising a top panel covering said container mouth, means forming an annularly disposed channel on the exteriorly facing surface of said top panel and slit vent means in said channel means for venting the container through said liner.

13. The liner of claim 12 in combination with an outer cap having a top panel, a skirt flange surrounding said mouth opening and attaching said cap to the container and a corner radius portion peripherally joining the top panel and skirt flange, an opening device in the top panel of said cap in overlying communication with said channel means, the opening device being operable for rupture of the top panel and removal of the cap from the container, said liner being disposed between said cap and mouth of the container, whereby differential pressure gas media in said container is conducted by said vent means and channel means to the point of initial opening in the top panel of the cap, and the container is vented upon operation of the opening device.

14. The closure article of claim 13, including means on opposite sides of the channel sealingly connecting the top panel of the liner to the under side surface of I the outer cap top panel.

15. The closure article of claim 14, wherein said sealingly connecting means comprises an annular planar surface defining concentric rings on either side of said channel and heat sealing attachment between the planar surfaces of said rings and the cap top panel.

16. The closure article of claim 14, wherein said sealingly connecting means comprises concentric annular ring patterns of adhesive material on the top surface of the liner top panel and disposed at either side of said channel thereon, said adhesive attaching the liner to the outer cap top panel.

17. The closure article of claim 13, including means for attaching said liner cap in nesting, concentric relationship within said outer cap, thereby providing a twopiece closure unit for capping assembly onto the mouth of the container.

18. A closure for sealing the mouth opening of a container for a product, said mouth being formed at a finish rim of the container, comprising a liner cap of an elastomeric material having a flexible, disc-like portion spanning the mouth opening of the container, slit valve means in said disc-like portion normally closed and operable in response to pressure differential on opposite sides of the disc-like portion for opening said valve means by flexing the disc-like portion on said finish rim, an outer cap having a top portion overlying said liner and a radial annular skirt portion surrounding the finish rim and securing the closure on the container, and a tear strip formed in said top portion of the outer cap, said strip traversing said slit valve means in the underlying disc-like portion of the elastomeric liner.

19. The closure defined in claim 18, wherein the top portion of the outer cap is domed to a convex configuration by pressurized gas conducted through said valve means of the liner providing a chamber between said liner and outer caps, said gas in the chamber being released upon severing said tear strip portion of the outer cap and said valve means thereafter venting the interior of the container by internal differential pressure flexing the disc-like portion convexly.

20. The closure defined in claim 18, including channel means annularly dis osed in said disc-like portion of the lmer cap, said sli valve means comprising axial slits through the elastomeric material and disposed in said channel means. I I

21. The closure defined in claim 20, wherein said channel means comprises an angular groove pin said disc-like portion and underlying said tear strip of the outer cap.

22. The closure defined in claim 18, wherein the outer cap is comprised of metal and the tear strip is integrally formed therein by a score line in said outer cap.

23. The closure defined in claim 22, wherein the outer cap is aluminum.

24. The closure defined in claim 22, wherein the elastomeric liner cap is comprised of polyethylene.

25. The closure defined in claim 18, wherein the outer cap comprises means for nestingly retaining the liner cap therein as a two-piece assembly prior to applying it on the container finish.

26. The closure defined in claim 25, wherein said means retaining said liner in the outer cap comprises an annular bead on the skirt of said outer cap disposed below the liner cap when the latter is nestingly assembled in the outer cap, said bead supporting said liner cap therein.

27. The closure defined in claim 25, wherein the means retaining said liner in the outer cap comprises an adhesive securing an area of the outer cap and liner cap together.

28. The closure cap defined in claim 27, including an annular channel in the disc-like portion of said liner cap and said adhesive is disposed on opposite sides of said channel.

29. The closure cap defined in claim 28, wherein said adhesive is disposed along said channel on its opposite sides and sealingly secures said liner to the outer cap.

" UNITED STATES PATENT OFFICE 5 CERTIFICATE OF CORRECTION Patent No. 119 Dated August 1972 h fl Robert O. Burroughs It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

:- Col. 2, line 3: "finished" should be -finish-; Col. 3, line 50: "attached" should be attach;

Col. 4, line 4: "pool" should be pull;

line 8: "29" should be 28--;

Col. 5, line 24: "produce" should be product;

Claim 21 (Col. 8, line 20) "pin" should be -in--.

Signed and sealed this 2nd day of January 1973'.

(SEAL) .Attest:

IZDWARI) M. lhl'lTCHliR Jlh ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 

1. A closure for sealing the mouth opening of a container for a pressurizable product, said mouth being formed by a finish rim of the container, comprising a liner having a disc-like portion covering the mouth opening of the container, said liner being comprised of an elastomeric material, channel means formed in said disc-like portion disposed annularly therein and radially inwardly of said finish rim, and plural, spaced apart vent slits axially through the material of said disc-like portion located in said channel means, each said vent slit and channel means cooperating through flexing of said material of said disc-like portion to open and close said vent slits for venting therethrough a pressure existing interiorly of the container, a cap having a top portion overlying said elastomeric liner and a radial annular integral skirt portion surrounding the finish rim and securing the closure on the container, and a rupturable convenience-opening tear strip formed in said top portion of the cap, said strip traversing at least one of said slits and channel means in the underlying disc-like portion of the elastomeric liner.
 2. The closure defined in claim 1, wherein the channel means comprises an annular groove in the top surface of said liner disc-like portion, said vent slits each being formed axially through the material in the bottom of the groove.
 3. The closure defined in claim 2, wherein the groove cross-sectional profile is arcuate.
 4. The closure defined in claim 3, wherein the annular groove is continuous.
 5. The closure defined in claim 4, wherein said vent slits are arc-segments in spaced array along said groove.
 6. The closure defined in claim 5, wherein the vent slits are of equal length and are at equally spaced apart intervals around said continuous arcuate groove.
 7. The closure defined in claim 1, wherein said channel means comprises a continuous arcuate groove depressed beneath the exterior surface of the liner top portion and provides a channel for conducting vented pressurized media from inside the container to a location beneath the initially ruptured portion of the tear strip of the outer cap upon opening the closure.
 8. The closure defined in claim 1, wherein the liner is attached to the underside of the cap on opposite radially disposed sides of the liner channel means.
 9. The closure defined in claim 8, wherein said attachment of liner and cap is by an adhesive applied for sealingly attaching the liner and cap on opposite sides of said channel means of the liner.
 10. An elastomeric snap cap liner for use in a closure on a container having a mouth opening defined by a finish rim comprising a top portion covering the mouth opening, a skirt flange surrounding said rim and joined peripherally at one side with the top portion at a corner radius, said corner radius overlying said container rim, groove means in the top surface of said top portion and disposed inwardly therein of said corner radius, and slit means through the top portion of said liner and disposed in said groove means.
 11. The elastomeric snap cap liner defined in claim 10, characterized by the fact that the slit means is openable by a pressure differential built up between the exterior and interior of the container to provide a vent for the container and closed when the pressure in the container is near atmospheric pressure.
 12. A liner for a closure covering a container mouth opening comprising a top panel covering said container mouth, means forming an annularly disposed channel on the exteriorly facing surface of said top panel and slit vent means in said channel means for venting the container through said liner.
 13. The liner of claim 12 in combination with an outer cap having a top panel, a skirt flange surrounding said mouth opening and attaching said cap to the container and a corner radius portion peripherally joining the top panel and skirt flange, an opening device in the top panel of said cap in overlying communication with said channel means, the opening device being operable for rupture of the top panel and removal of the cap from the container, said liner being disposed between said cap and mouth of the container, whereby differential pressure gas media in said container is conducted by said vent means and channel means to the point of initial opening in the top panel of the cap, and the container is vented upon operation of the opening device.
 14. The closure article of claim 13, including means on opposite sides of the channel sealingly connecting the top panel of the liner to the under side surface of the outer cap top panel.
 15. The closure article of claim 14, wherein said sealingly connecting means comprises an annular planar surface defining concentric rings on either side of said channel and heat sealing attachment between the planar surfaces of said rings and the cap top panel.
 16. The closure article of claim 14, wherein said sealingly connecting means comprises concentric annular ring patterns of adhesive material on the top surface of the liner top panel and disposed at either side of said channel thereon, said adhesive attaching the liner to the outer cap top panel.
 17. The closure article of claim 13, including means for attaching said liner cap in nesting, concentric relationship within said outer cap, thereby providing a two-piece closure unit for capping assembly onto the mouth of the container.
 18. A closure for sealing the mouth opening of a container for a product, said mouth being formed at a finish rim of the container, comprising a liner cap of an elastomeric material having a flexible, disc-like portion spanning the mouth opening of the container, slit valve means in said disc-like portion normally closed and operable in response to pressure differential on opposite sides of the disc-like portion for opening said valve means by flexinG the disc-like portion on said finish rim, an outer cap having a top portion overlying said liner and a radial annular skirt portion surrounding the finish rim and securing the closure on the container, and a tear strip formed in said top portion of the outer cap, said strip traversing said slit valve means in the underlying disc-like portion of the elastomeric liner.
 19. The closure defined in claim 18, wherein the top portion of the outer cap is domed to a convex configuration by pressurized gas conducted through said valve means of the liner providing a chamber between said liner and outer caps, said gas in the chamber being released upon severing said tear strip portion of the outer cap and said valve means thereafter venting the interior of the container by internal differential pressure flexing the disc-like portion convexly.
 20. The closure defined in claim 18, including channel means annularly disposed in said disc-like portion of the liner cap, said slit valve means comprising axial slits through the elastomeric material and disposed in said channel means.
 21. The closure defined in claim 20, wherein said channel means comprises an angular groove pin said disc-like portion and underlying said tear strip of the outer cap.
 22. The closure defined in claim 18, wherein the outer cap is comprised of metal and the tear strip is integrally formed therein by a score line in said outer cap.
 23. The closure defined in claim 22, wherein the outer cap is aluminum.
 24. The closure defined in claim 22, wherein the elastomeric liner cap is comprised of polyethylene.
 25. The closure defined in claim 18, wherein the outer cap comprises means for nestingly retaining the liner cap therein as a two-piece assembly prior to applying it on the container finish.
 26. The closure defined in claim 25, wherein said means retaining said liner in the outer cap comprises an annular bead on the skirt of said outer cap disposed below the liner cap when the latter is nestingly assembled in the outer cap, said bead supporting said liner cap therein.
 27. The closure defined in claim 25, wherein the means retaining said liner in the outer cap comprises an adhesive securing an area of the outer cap and liner cap together.
 28. The closure cap defined in claim 27, including an annular channel in the disc-like portion of said liner cap and said adhesive is disposed on opposite sides of said channel.
 29. The closure cap defined in claim 28, wherein said adhesive is disposed along said channel on its opposite sides and sealingly secures said liner to the outer cap. 